linux-kernel - Re: [GIT PULL] perf changes for v3.8

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Date:	Mon, 24 Dec 2012 12:36:20 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	David Ahern <dsahern@...il.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [GIT PULL] perf changes for v3.8

On Sun, Dec 23, 2012 at 04:17:45PM -0700, David Ahern wrote:
> On 12/23/12 2:23 AM, Gleb Natapov wrote:
> >>Your patch alone was not enough. Start here:
> >>  https://lkml.org/lkml/2012/7/12/3
> >>
> >I cannot reproduce this failure. I reverted 20b279ddb38c and ran "perf
> >record -e cycles:ppG" while guest was running. Admittedly I ran the test
> >for a short time, but without disabling PEBS during the guest entry this
> >was enough to crash a guest.
> 
> In the beginning (without any patches) VMs crashed fairly quickly.
> With your patch it took longer, but I was able to consistently crash
> VMs. The thread notes server info (processor, OS) and VM versions as
> well as load used for the tests -- a cpu bound process (openssl),
> disk bound (dd) and network (netperf).
> 
> 
It means that disabling PEBS is not enough and PMU counter should be
disabled too.

> >What about forcing exclude_guest on an event that
> >has precise flag set without reporting error to userspace?
> 
> That's up to the perf maintainers -- Ingo, Peter, Arnaldo.
> Personally, I don't like it since kernel side is changing the user
> request.
> 
I do not see other way to prevent guests from crashing with older perf
binaries if 20b279ddb38c will be reverted.

--
			Gleb.
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